Let's suppose that we create an application to fetch
data from the above XML document and produce this output:

E-mail

To:Rohan
From: Amit

Be ready for a cruise...i will catch u
tonight

Now, the author wants to add a new feature (let it be a
subject line). He can easily achieve it by adding one more tag ie..<Subject>in
the xml document. So the new modified xml document will look like this :

Here, E-mail is the root element
while To, From, Subject and Body are the child elements
of the E-mail. Here, E-mail is the parent element
of To, From, Subject and Body. To, From, Subject and Body are siblings
(or sister elements) because they have the same parentage.Hence , all the XML Elements have Relationships.

XML Element Naming : Know-hows

XML elements must follow these naming conventions:

Names must not start with a number or punctuation
character but it can contain letters, numbers, and other
characters without spaces.Names must not start with the letters xml (or XML,
or Xml, etc)